Method of housing corrosive electrolytic medium



y ,197o R.|' .NOVACK 3,514,333

METHOD OF HOUSING CORROSIVE ELECTROLYTIC MEDIUM Filed June 20, 1967 ROBERT LEE NOVACK, INVENTOR.

BYRQNZAMQAAM ATTORNEYS 3,514,333 Patented May 26, 1970 3,514,333 METHOD OF HOUSING CORROSIVE ELECTROLYTIC MEDIUM Robert Lee Novack, Hanover, Mass., assignor to Prototech Company, division of Bolt Beranek and Newman Inc., Cambridge, Mass., a corporation of Massachusetts Filed June 20, 1967, Ser. No. 647,479 Int. Cl. H01m 1/02, 27/00; B65d 53/00 U.S. Cl. 136-86 6 Claims ABSTRACT OF THE DISCLOSURE The problem of sealing a removable wall (such as a top cover) of a corrosive electrolytic mediumcontaining housing, as in fuel cells and similar apparatus, has been solved through a novel use of a thin aluminum sealing gasket maintained at a temperature suflicient to soften the aluminum without melting the same and high enough to maintain the electrolytic medium molten and essentiallyanhydrous, with the gasket being subjected to appropriate uniform sealing pressure.

The present invention relates to the problem of sealing housings containing corrosive electrolytic media and the like, particularly those being operated as in fuel and similar cells at high temperatures.

This sealing difilculty has plagued the art for some time in view of the inability of even high-temperature ceramics, plastics, alloys and other materials reliably to resist for prolonged periods the corrosive action of electrolytic media and the like under conditions of closed-housing, high-temperature operation. Such prior seals under continued long-term operation invariably develop cracks or leaks or are corrosively detrimentally attacked and require relatively frequent replacements and repair.

In my co-pending application, Ser. No. 376,917, filed June 22, 1964, which is now abandoned, for Method of and Apparatus for Containing Alkali-Metal Hydroxides and Carbonates, it is explained that though it has long been accepted that aluminum is readily attacked in aqueous alkali-metal hydroxide solutions, forming a precipitate of aluminum hydroxide or forming aluminates, a discovery has been made that enables the utilization of aluminum for containing alkali metal hydroxides and carbonates and the like without such corrosive attack. Similarly, the ready dissolution of aluminum in hot concentrated solutions of alkali-metal carbonates, including sodium carbonate, has long been known; such that the art has considered aluminum a most unsatisfactory metal for use in systems in which it must come into contact with alkali-metal hydroxides or carbonates. In the alkali electrolyte fuel cell field, for exampe, it has even been reported that auminum cannot stand up to such electrolyte, particularly at elevated temperatures.

As disclosed in said co-pending application, however, if molten alkali-metal hydroxides and carbonates are maintained at temperatures between about 300C. and 500 C., more or less, and the water content thereof is allowed to decrease until it approaches substantial equilibrium with the moisture in the air or other medium surrounding the melt, aluminum, preferably substantially pure (although aluminum with some impurities and alloys thereof have been found to exhibit some of the resistant characteristics herein described), can be placed in direct and continuous contact with the corrosive molten alkali-metal hydroxides and carbonates without suffering any appreciable corrosion.

In summary, it has now been discovered that, particularly in corrosive electrolytic media maintained at about the temperatures above discussed, sufiiciently thin aluminum strips possess softening and other properties as well that, if employed under proper pressure and other conditions, can extend the use of aluminum for indefinite sealing purposes, still without corrosive attack or failure.

An object of the invention is thus to provide a new and improved housing and sealing structure for high-temperature electrolytic media and the like.

A further object is to provide a novel aluminum seal construction of more general use, also.

Other and further objects will be explained hereinafter and are more particularly pointed out in the appended claims.

The invention will now be described with reference to the accompanying drawing, the single figure of which is an exploded fragmentary isometric view illustrating a preferred application of I the invention to fuel cell housings and the like.

Referring to the drawing, with the understanding that this is but an illustration of one of the numerous applications of the invention, a fuel cell or similar housing is shown at 1 havingan internal electrolytic medium-containing chamber, generally designated at 3. In the case of the alkali-hydroxide media above-mentioned; for example, the electrolytic medium may comprise-a mixture of potassium and sodium hydroxide maintained molten and essentially anhydrous at the above-discussed temperatures by any conventional temperature-controlling apparatus, diagrammatically designated by the arrow labeled HEAT.

The bounding walls of the housing may be of nickel or similar material which resists corrosive attack by such high-temperature molten electrolytic media, and may be closed off by a top wall or cover 1" of the same material. The top wall 1" is shown carrying the fuel and oxidant inlets 4 and 2 and a vent 10, each inlet having a smaller feed pipe 4' and 2', respectively, for providing fuel and, for example, air to the electrolytic medium 3. The fuel may be pure or impure hydrogen, for example, or a carbon-and-hydrogen-containing fuel that may be reformed within an anode chamber 6 into hydrogen as described, for example, in US. Letters Patent No. 3,206,- 334. The anode structure 6 is shown faced by a palladiumoontaining or other hydrogen-permeable but otherwise non-porous anode layer 8 on one side (to the right), and preferably a similar parallel layer (not shown) on the other side (to the left). The air introduced at 2' will cause stirring action to insure adequate peroxide or superoxide oxidant at the cathode portions of the cell effectively provided by the nickel walls of the housing itself. Other conventional details are omitted so as not to detract from the novel features of the invention.

To solve the problem of providing a high-temperature, non-corrosive, non-cracking and leak-proof seal for the cover wall 1", a thin aluminum frame gasket 5 is provided, supported by a lateral flange portion 1' extending outward from the plane of the side walls of the housing 1, and adapted to be pressurized by securing elements 7 bolted or otherwise fastened within corresponding apertures 7 in the cover 1" and distributed to provide uniform sealing pressure on the thin and narrow aluminum gasket 5 about the peripheral borders of the wall flange 1' and the outer peripheral underside portions of the cover wall 1".

Fortuitously, at temperatures of about 400 to 600 C., which are excellent for keeping the medium 3 anhydrous and molten (and thus as described in said co-pending application, unable to attack the aluminum) the thin and narrow aluminum frame gasket 5, which may also be a wire loop of similar dimensions, has been found to soften but not melt if maintained at thicknesses of the order of .010.050", more or less. By keeping the frame gasket 5 narrow, preferably of the order of A; more or less, pressure in the range of about 1000-5000 lbs/in. can be brought to bear substantially uniformly about the gasket. In view of the greater coefficient of expansion of such an aluminum gasket than that of the nickel housingwalls, it has been found that such pressure, temperature and other above described structural conditions, enable the aluminum gasket 5 to effect a remarkable seal for thousands of hours of high-temperature closed-housing operation, without leaking and without corrosive attack.

Further modifications, including uses of different fuel and other cell configurations, electrolytic media and apparatus, will also occur to those skilled in this art and all such are considered to fall within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. A method of housing a corrosive electrolytic medium of the group consisting of alkali-metal hydroxides and carbonates, which comprises bounding said medium with walls of material resistant to said medium at least one of which is removable and closable relative to the others, interposing a thin. .aluminum gasket between .the adjacent peripheral borders of said one wall and mating portions of the remaining walls, maintaining the temperature of said medium at a value in the range of about 400 to 600 degrees C. and sufilcient to render the medium substantially molten and anhydrous and suflicient to soften the aluminum gasket without melting it, and applying pressure between said peripheral borders and mating portions substantially uniformly thereabout to efiect sealing action of said aluminum gasket therebetween.

2. A method in accordance with claim 1, in which the medium is bounded by walls of material having less coeflicient of expansion than aluminum.

3. A method in accordance with claim 1, in which the pressure applied is in excess of about 1,000 lbs. per square inch.

4. A method in accordance with claim 1, in which the medium is bounded by walls of nickel.

5. A method in accordance with claim 1, in which said mating portions are provided with a flange extending laterally outward from the walls thereof and the gasket is disposed upon said flange.

6. A method in accordance with claim 1, in which the gasket provided is of the order of 0.010.050 inch thick.

References Cited UNITED STATES PATENTS 3,042,248 7/1962 Krueger 22046 3,315,836 4/1967 Boon 22046 3,378,404 4/1968 Diotalevi et a1. 136-86 3,387,738 6/1968 Kemp 22046 WINSTON A. DOUGLAS, Primary Examiner D. L. WALTON, Assistant Examiner US. Cl. X.R. 

